active transport

Different types of transport across a cell membrane. Diffusion and osmosis are passive modes of transport, requiring no energy, moving from areas of high concentration to areas of low concentration. Active transport requires energy to transport molecules from low concentration to high concentration.

Movement of molecules or ions across a cell membrane using energy provided by respiration. Examples of substances that can be actively transported across membranes are sodium ions and glucose.

Energy is needed because the movement occurs against a concentration gradient, with substances being moved from an area of low concentration to an area where there is a higher concentration. Active transport is therefore quite different from diffusion, which requires no input of energy. In diffusion the movement is in the opposite direction – from an area of high concentration to an area where the concentration is low. An example of diffusion is the movement of oxygen into the blood vessels of the lungs.